1. Field of the Invention
The present invention pertains generally to passive microwave structures using a thick film construct, and more particularly to a thick film balanced line structure for use in the construction of microwave mixers, power splitters, and filters.
2. Description of the Background Art
Microwave balanced line structures have been fabricated from many types of mediums. For example, three-dimensional structures have been typically fabricated from thin ceramic, PTFE, soft board, or Teflon.RTM.-based dielectric materials suspended in air, using various twisting techniques to fabricate the substrate. For typical structures having an impedance of 50 ohms, however, the line widths range from 0.020 to 0.030 inches which makes it difficult to place long line structures in a small area. Further, assembly is tedious and requires manual labor, and the thin dielectric materials used do not lend themselves to automated manufacturing or commonly used surface mount assembly techniques. At lower frequencies these structures are constructed using twisted copper wire wrapped around ferrite core materials. However, these structures are large and bulky, involve manual assembly techniques, and do not work well at microwave frequencies. Another type of known balun, as described in U.S. Pat. No. 4,954,790, uses a multilayer approach on thin film, with edge coupled lines requiring tight tolerances and exacting construction. Although this structure lends itself well to surface mount construction, it is expensive to manufacture.
Because balanced line structures are used in the construction of microwave mixers, power splitters and filters, there is need for a balanced line structure which is low in cost, repeatable to manufacture, and compatible with commonly used surface mount assembly techniques. The present invention satisfies that need, as well as others, and overcomes the deficiencies found in the previously developed devices.